Cubic Regression?

Question

my TI-89 is giving me some domain error for no reason.

Can someone please give me the formula for the cubic regression of
L1: 0, 3, 6, 9, 12, 15, 18
L2: 50, 65.5, 70, 66, 58, 51, 48

Answer 1

y = a + bx + cx^2 + dx^3
|. n. . ∑x. . ∑x^2 ∑x^3| |a| |.. ∑F. |
|∑x. . ∑x^2 ∑x^3 ∑x^4| |b| |. ∑xF |
|∑x^2 ∑x^3 ∑x^4 ∑x^5| |c| |∑x^2F|
|∑x^3 ∑x^4 ∑x^5 ∑x^6| |d| |∑x^3F|

This sets up nicely on a spreadsheet. Your values yield

a = 49.9047619
b = 7.739417989
c = -0.889550265
d = 0.025205761

y ≈ 50 + 7.74x - 0.89x^2 + 0.0252x^3